Self-assembled hydrated copper coordination compounds as ionic conductors for room temperature solid-state batteries

As the core component of solid-state batteries, neither current inorganic solid-state electrolytes nor solid polymer electrolytes can simultaneously possess satisfactory ionic conductivity, electrode compatibility and processability. By incorporating efficient Li+ diffusion channels found in inorganic solid-state electrolytes and polar functional groups present in solid polymer electrolytes, it is conceivable to design inorganic-organic hybrid solid-state electrolytes to achieve true fusion and synergy in performance. Herein, we demonstrate that traditional metal coordination compounds can serve as exceptional Li+ ion conductors at room temperature through rational structural design. Specifically, we synthesize copper maleate hydrate nanoflakes via bottom-up self-assembly featuring highly-ordered 1D channels that are interconnected by Cu2+/Cu+ nodes and maleic acid ligands, alongside rich COO− groups and structural water within the channels. Benefiting from the combination of ion-hopping and coupling-dissociation mechanisms, Li+ ions can preferably transport through these channels rapidly. Thus, the Li+-implanted copper maleate hydrate solid-state electrolytes shows remarkable ionic conductivity (1.17 × 10−4 S cm−1 at room temperature), high Li+ transference number (0.77), and a 4.7 V-wide operating window. More impressively, Li+-implanted copper maleate hydrate solid-state electrolytes are demonstrated to have exceptional compatibility with both cathode and Li anode, enabling long-term stability of more than 800 cycles. This work brings new insight on exploring superior room-temperature ionic conductors based on metal coordination compounds.


Supplemental Figures and Tables
As shown in Fig. S5a, the characteristic peaks in the 1 H NMR spectrum of the pristine CuMH sample are assigned to resonances of hydroxyl hydrogens (-COOH) [1] and the methylene protons (-CH=CH-) [2] , respectively.After the hydrogen/deuterium (H/D) exchange reaction, the peaks appearing at 6.2 and 5.5 ppm are identified to resonances of the methylene protons (-CH=CH-) and protons of HOD, while the peak at 12.1 ppm completely disappears, convincingly demonstrating the existence of hydroxyl hydrogen (-COOH) in the CuMH sample.Moreover, the 1 H NMR spectrum of the Li-CuMH sample only shows one characteristic peak of the methylene protons (-CH=CH-) at 6.2 ppm, since the H + ions on the carboxylic acid of CuMH underwent an ion-exchange reaction with the Li + ions during the soaking process (Fig. S5b).Lifetime: The end-of-life criterion is defined as 80% of capacity retention or short circuit [10] .
Figure S1.Digital photographs of the production speed of CuMH powders at different reaction times a) without and b) with the addition of LiNO3.The production speed of CuMH has been greatly accelerated with the aid of LiNO3, while the reaction rate without LiNO3 is extremely low.

Figure S2 .
Figure S2.SEM image of irregular CuMH nanosheets obtained from the traditional solvothermal method using Cu(NO3)2 as the precursor.

Figure
Figure S3.a) Cu 2p XPS and b) Cu Auger LMM spectra of CuMH film prepared from MA and Cu 0 foil.The raw data and fitted data plots are shown as gray hollow points and grey solid lines, respectively.

Figure
Figure S4.a) Cu 2p XPS and b) Cu Auger LMM spectra of CuMH film prepared from

Figure
Figure S5.a) 1 H NMR spectra of original CuMH sample and the CuMH sample after hydrogen/deuterium (H/D) exchange.b) 1 H NMR spectra of the Li-CuMH sample.

Figure S6 .
Figure S6.Powder XRD pattern of the as-obtained CuMH powder and single crystal XRD pattern of sample grown in water and the corresponding standard powder diffraction card (PDF#49-2453).

Figure S7 .
Figure S7.Rietveld refinement patterns of XRD for the Cu Ⅰ/Ⅱ MH (a) and Li-Cu Ⅰ/Ⅱ MH (b) samples.The observed and calculated intensities are shown as the red circles and the black solid line, respectively.The bottom blue line exhibits the fitting residual difference.The Bragg positions are represented by purple scale lines.

Figure S8 .
Figure S8.Local structures of Cu + and Cu 2+ coordinated with maleic acid in the CuMH crystal, respectively.

Figure S9 .
Figure S9.The crystal structure of CuMH containing Cu + and Cu 2+ along the c-axis.

Figure S10 .
Figure S10.Schematic diagram of a roller press for rolling the CuMH-PTFE paste into compact film.

Figure S11 .
Figure S11.Top view and side view SEM images of the Li-CuMH SSE film.

Figure S12 .
Figure S12.The crystal structure of Li-CuMH produced by the ion-exchange reaction between Li + ions and H + from CuMH.a) The crystal structure of CuMH.b) The crystal structure of Li-CuMH.

Figure S14 .
Figure S14.The SAXS curves a) of CuMH and Li-CuMH, and the corresponding zoom-in curves in the q range of b) 0.8-0.95Å and c) 1.35-1.6Å, respectively.The corrected scattering intensity was plotted relative to the scattering vector q.

Figure
Figure S15.a) XRD patterns of CuMH film and Li-CuMH SSE film and b) the corresponding enlarged spectra in the 2-theta range of 11.5° and 13°.

Figure
Figure S16.a) XRD patterns of Li-CuMH SSE films after soaking in the non-aqueous electrolyte containing LiTFSI salts for different times and b) the corresponding enlarged spectra in the 2-theta range of 11.5° and 13°.

Figure
Figure S17.a) Nyquist plots of Li-CuMH SSE films with different Li + implantation times and b) the corresponding ionic conductivities at room temperature.

Figure S18 .
Figure S18.TGA curves of CuMH powder, CuMH film and Li-CuMH film.All samples remained stable until the temperature reaches 100 ℃, and then gradually dehydrated in the temperature range of 100-160 ℃.This directly demonstrates that the

Figure S19 .
Figure S19.Electrostatic potential (ESP) distribution of maleate unit and structural water in Li-CuMH.

Figure S20 .
Figure S20.1D Li + ion migration path in the direction of the [010] chain along the baxis (green dotted line).

Figure S21 .
Figure S21.2D Li + ion migration path in the bc plane.

Figure S24 .
Figure S24.XRD patterns of CuMH powders after sintering at 200 °C for different times.

Figure S25 .
Figure S25.Digital images of chemical stability and side reactions of Li metal electrodes after contact with Li-CuMH SSE and organic liquid electrolyte for different times.

Figure S28 .
Figure S28.FT-IR spectra in the region of TFSI -vibration of 1M LiTFSI in DOL/DME liquid electrolyte and Li-CuMH SSE.

Figure S29 .
Figure S29.Arrhenius plots of the organic liquid electrolyte, Li-CuMH SSE and solid polymer PEO electrolyte.

Figure S30 .
Figure S30.Li + transference number measurement of a) the organic liquid electrolyte and b) solid polymer PEO electrolyte.The insets are the Nyquist plots of Li/liquid electrolyte/Li and Li/PEO electrolyte/Li symmetric cells before and after polarization, respectively.

Figure
Figure S31.a) Voltage profiles of the Li/Li symmetric cells assembled with liquid electrolyte (1M LiTFSI in DOL/DME), PEO electrolyte and Li-CuMH SSE at the current density of 0.2 mA cm -2 and areal capacity of 0.1 mAh cm -2 .b-d) The enlarged voltage profiles highlighted in the I, II and III regions of a).

Figure
Figure S32.a) Nyquist plot and b) impedance phase angles versus frequencies plot of the Li/Li-CuMH SSE/Li symmetric cell before cycling at room temperature ranging from 10 5 to 10 -2 Hz.The inset in a) is the corresponding equivalent circuit used to fit the Nyquist plot, in which Rb represents the bulk resistance, RSEI is the SEI resistance, RCT stands for charge-transfer resistance, CPESEI is the capacitance of SEI, CPECT is the capacitance describing the electrical double layer at the SSE/Li interface, and W is the Warburg impedance (linear line).

Figure S36 .
Figure S36.The long-term cycling of LFP/PEO electrolyte/Li full batteries, in which the EO: Li was 10:1.(a) The specific discharge capacity of LFP/PEO electrolyte/Li full batteries during 60 cycles at 0.5 C and 60 °C.(b) The charge/discharge curves of LFP/PEO electrolyte/Li full batteries at 1 st , 20 th , 30 th , 40 th , and 50 th cycles at 0.5 C and 60 °C, respectively.

Figure S37 .
Figure S37.Long-term cycling performance of LFP/liquid electrolyte/Li full batteries, wherein liquid electrolyte was 1M LiTFSI in DOL/DME.a) Cycling stability of the LFP/liquid electrolyte/Li full cell during 200 cycles at 0.5 C and room temperature.b) Charge/discharge profiles of the LFP/liquid electrolyte/Li full cell at 1 st , 20 th , 50 th , 100 th , and 200 th cycles at 0.5 C and room temperature, respectively.

Figure S38 .
Figure S38.CV profiles of the LFP/Li full batteries with the liquid electrolyte (the upper panel) and Li-CuMH SSE (the bottom panel) at 0.1 mV s -1 .

Figure S39 .
Figure S39.SEM images of Li metal anodes disassembled from Li/Li symmetric cells with a-b) Li-CuMH SSE and c-d) organic liquid electrolyte after 200 cycles, respectively.

Figure S40 .
Figure S40.2D AFM images of SEI layers on Li metal anodes disassembled from Li/Li symmetric cells with a) Li-CuMH SSE and b) organic liquid electrolyte after 200 cycles.

Figure
Figure S41.a) 3D AFM image and b) the corresponding force-separation curve of Li anode disassembled from Li/Li symmetric cell with liquid electrolyte.

Figure S42 .
Figure S42.F 1s, N 1s and C 1s in-depth XPS spectra of SEI layers on Li anodes disassembled from Li/Li symmetric cells with liquid electrolyte.The raw data and fitted data plots are shown as gray hollow points and grey solid lines, respectively.

Figure S43 .
Figure S43.O 1s and Li 1s in-depth XPS spectra of SEI layers on the surface of Li metal anodes disassembled from Li/Li symmetric cells with a) Li-CuMH SSE and b) organic liquid electrolyte.The raw data and fitted data plots are shown as gray hollow points and grey solid lines, respectively.

Figure S44 .
Figure S44.Quantitative surface composition of SEI layers on Li anodes disassembled from Li/Li symmetric cells with Li-CuMH SSE and liquid electrolyte.

Table S1 .
Structural analysis results obtained from Rietveld refinement XRD patterns of the Cu Ⅰ/Ⅱ MH and Li-Cu Ⅰ/Ⅱ MH samples.

Table S2 .
Supplementary Note: The Li + transference number (tLi+) was measured on Li/Li-CuMH SSE/Li symmetric cells by the chronoamperometry test.The Li + transference number were calculated by the equation (2): IO, ISS, RO and RSS represent the applied voltage (10 mV), the initial and steadystate currents and the impedance before and after polarization, respectively.As show in FigureS30a, IO, ISS, RO and RSS are 120 μA, 93μA, 78 ohms and 87 ohms, respectively.Thus, the Li + transference number of the liquid electrolyte is 0.26.Similarly, the Li + transference number of the PEO electrolyte is calculated as 0.16.The parameters measured by i-t curves and EIS for calculating the Li + transference number.This table refers to Figs. 3g and S30.
Io and Iss are initial and stable current (μA) during polarization.Ro and Rss are the impedance (ohm) before and after polarization.

Table S3 .
Li/Li symmetric cell performance of Li-CuMH SSE and SSEs in the literatures.This table refers to Figure 4b.

Table S4 .
The values of Rb, RSEI, Rct, and RSSE/Li obtained by fitting each individual spectrum of Li/Li-CuMH SSE/Li symmetric cells after various cycle numbers at 0.5 mA cm -2 .

Table S5 .
Comparision of electrochemical performance of LFP/Li batteries with the Li-CuMH SSE, liquid electrolyte and solid polymer PEO electrolyte.This table refers to

Table S6 .
Comparison of electrochemical performance of LFP/Li batteries with the Li-CuMH SSE and SSEs previously reported in the literatures.